This is going to read like a story and I apologize for that but I figure this is the best way to report my observations.
Ariens: 936046
Serial: 041910C012688
Briggs: 31G777 1413 B1 091103ZD
This came to me because it wouldn't start. It is owned by a woman who is not very mechanical. The first thing I noticed was a huge mouse next under the cover on top of the cylinder. I'm told that it has cut the lawn 3 or 4 times this season like this. About a 1/2 acre. The first thing I did is remove the mouse nest and clean it out. I checked the valves and did a leak down and noticed a bit escaping from the intake. But I wanted to see if it would run so I didn't go any deeper than cleaning it out. It came to me with decent looking oil but the level was at the bottom line. So I added to get to the right level. Once cleaned and with the proper amount of oil, I started it up and it started just fine and ran great for about a minute. It's very likely that the owner, who inherited this and is not very knowledgeable, just didn't know how to start it correctly. But once I noticed the mouse nest, I wanted to get it squared away before trying to run it.
During cleaning it out, I noticed some black tar-like substance on the metal shield under the flywheel. I was thinking that maybe they overheated it and either blew some out the seal under the flywheel, or it was just old oil that tarred up from the engine running too hot with the mouse nest.
Once all cleaned up, I started it up with the intention of warming up the oil for a change and let it run for about 4 minutes, at which point I started smelling something burning, not a smell I've noticed in the past. It was kind of like a burning rubber smell but not quite. I did see some thin smoke in my garage and the smell was pretty bad. I figured it was that tar and maybe some dirt / oil burning off. but it got pretty bad and I started noticing it not quite running right. She turned a little rough and I shut it down. This may have been in my head but given the smell, I became hesitant to let it run any more. Once it shut down, I turned the flywheel by hand and things seemed good. Started it again for a second with no problem after a few minutes. I have a laser therm and can check the temp on the engine if that info helps. I wish I could describe the smell a little better.
I got the right amount of decent oil in this. I'm not sure how to proceed. Is this the old burnt oil burning off the engine or do I have a bigger problem here? I know this is a tough question but thought I'd report my observations and see if it rings a bell for anyone.